Fitment issues with 285 35 18 69 DSE

[colorado80439]

So I'm in the middle of a build with a 69 Camaro DSE subframe hanging the fenders and modding the inner fenders. I have an 18x10 rim 6.25 backspace and a 285/35/18. The car is on jack stands and we pulled the shocks off to look at fitment through the full range of travel. If I raise the tire into the fender about 1 inch from the upper bump stop, I can only turn the wheel through less than half it's turn radius before it hits the fender at about the 2 o'clock or 10 o'clock position depending on the direction I'm turning the wheel. They are GM fenders, planning to roll the lip which will give a little more. The camber is set to DSE's initial set up which definitely negative. Spoke with DSE and they recommend a 275/35/18 with 6.125 backspace and they say with the 275 set up it will probably rub in some situations, but again I'm only getting half my turn radius when compressed 1 inch from the top bump stop. Is this normal? Will I never be that compressed when into a hard turn?
Thanks in advance, Dave